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Shepherd FTIR

The Cerex Shepherd FTIR provides real-time laboratory quality measurements within a portable package to achieve exceptional versatility


A true multi-gas analyzer, the Shepherd FTIR standard gas detection libraries are built for common applications, including: air toxics monitoring, hospital and anesthetic gas monitoring , and refinery monitoring. The Shepherd FTIR is also capable of simultaneous monitoring of more than 350 compounds in Cerex’s FTIR library.

Offering true part-per-billion (ppb) detection limits in a simple to operate portable package, the Cerex cryo-cooled system can reliably deliver unattended, continuous real time monitoring of ultra low ppb concentrations of individual gas species with absorption features spanning the IR spectrum from 2 to 14 microns. There are no tedious ongoing calibrations, or additional costs for sample handling, wet chemistry, carrier gas, or sorbent filters. Additionally, are none of the constant maintenance costs or extra work associated with the handling of, or regulatory compliance issues arising from the use of, liquid nitrogen coolant, and with a three year routine maintenance cycle there is a low cost of ownership and time spent. Results are immediate, and the raw data containing all the information necessary for gas identification and quantification is always saved.

How it WorksFTIR

Fourier transform infrared spectroscopy (FTIR) is the preferred technique used to obtain an infrared spectrum of absorption or emission of a solid, liquid, and gas.

The Shepherd FTIR operates by sending a beam of infrared light through a 20 meter sealed sample cell within the instrument. The IR beam is directed by a series of optics to an ultra-sensitive cryo-cooled MCT detector where minute changes in IR absorption are sensed due to trace concentrations of individual gases. A classical least squares regression analysis compares the measured absorption spectrum to calibrated reference absorption spectra files. Beer’s law is then used to determine gas concentrations (Beer-Lambert Law).

The result of coupling our proven detection system with a 20 meter internal optical sample path and CMS real time analytic software is an industry leading FTIR multi-gas analyzer.

Cerex’s Shepherd FTIR analyzers feature:

  • Convenient portability on wheels
  • PPB Detection Limits
  • Continuous, real time monitoring of 385 individual gas species
  • Cryo-cooled MCT Detector
  • 0.5 Wavenumber Resolution
  • Integrated Ethernet / WiFi
  • PC or Smartphone Remote Control
  • 4+ hour battery run-time
  • Automatic saved records of data
  • Customizable audible, visual and email alerts

All Shepherd FTIR analyzers come standard in a weather-resistant case with an integrated computer, touchscreen display, active ambient air sampling, and integrated WiFi.

Shepherd FTIR Applications

  • Ambient Air Monitoring
  • Anesthetic / Hospital Monitoring
  • Chemical Manufacturing AQ
  • Chemical Warfare Agent Detection
  • Container Inspection
  • General Industrial Air Monitoring
  • Indoor Air Monitoring
  • Leak Detection
  • Manufacturing Air Quality
  • Odor Complaint Response
  • Refinery Air Quality Fertilizer
  • Response Border Patrol Inspection
  • Stationary Source Monitoring (Cool, dry sample)

Note: Open Path FTIR is not recommended for Benzene and Hydrogen Sulfide monitoring due to poor detection limits; instead, we recommend our UV Sentry, AirSentry FTIR, or UV Hound Series analyzers

Shepherd FTIR Model

Extensive Library with Options for Customization


Cerex has over 385 compounds available for detection with the Shepherd FTIR. If your compound is not one of the compounds already available within our database, the Cerex Shepherd FTIR may import gas spectra from the numerous FTIR databases on the web (NIST, EPA, PNNL, etc.)

If you have a compound that is not available in a public database, we may be able to work with you to develop a custom spectrum. Detection limits are a function of the IR detector, installed path length, and site conditions. The detection limits shown have been empirically determined from bump tests of fielded instruments at full path-length.

Type Compound MDL PPB
Criteria Sulfur Dioxide 300
Volatile Organic Compounds Acrolein 15
1,3 Butadiene 4
Styrene 8
BTEX Benzene 30
Toluene 100
Ethylbenzene 25
m-Xylene 100
o-Xylene 300
p-Xylene 300
Alkanes Pentane C5 4
n-Hexane C6 3
TVOC Methane C1 3
NMHC Ethane C2 8
NMNEHC Butane C4 4
Propane C3 4
Formaldehyde 7
Propene (propylene) 6
Ethene (ethylene) 4
Acetylene 4
Acetaldehyde 5
Methanoic Acid 5
Methanol 4
Other Hydrogen Cyanide 10
Hydrogen Fluoride 4
Ammonia 3
Hydrogen Sulfide 450

Shepherd FTIR Specifications

General Parameters
Part Number Shepherd FTIR
Analyzer Type Multi-gas portable point analyzer
Technology Fourier Transform InfraRed (FTIR) Differential Optical Absorption Spectroscopy (DOAS)
Performance Available with standard HAP (385 compound & 62 Compound), Criteria, Hospital and custom gas detection libraries.
Data Output Rate User selectable from 5 seconds and up
Typical output rates are 30s, 60s, 120s, or 300s
Time weighted average available for user defined periods (8 hour, 12 hour, 24 hour)
Measurement Principle Beer-Lambert Law
Measurement Technique Classical Least Squares (CLS) regression analysis; optional Partial Least Squares (PLS)
Operating Temperature 0°C to 35°C (Optional Air Cooled Model)


Storage Temperature -40C° to 60C°
Power Supply 100 to 130V or 200 to 240VAC/50-60Hz
Power Consumption 240W MAX
Instrument Cooling Air Cooled
Installation Fixed mount or tripod mount (open path analyzer mode)
Bench-top (point analyzer mode)
Dimensions 42.1″ x 21.9″ x 23.3″ (107cm x 55.7cm x 59.1cm)
Weight 85 lbs (38.6Kg)
Measuring Parameters
Concentration measurement accuracy ±5 % Reading TYP
Concentration measurement precision ±5 % Reading TYP
Interferent Mitigation Real time spectral subtraction and residual subtraction, multi-peak analysis.
Zero point calibration Simultaneous dual mode natural zero and/or synthetic zero on gas by gas basis. Automated compound specific background selection.
Real Time Operating Software Cerex Continuous Monitoring Software (CMS)
Operating System Windows 10 Pro
Post Collection Analysis Software Cerex Data Processor
Operating System Windows 7, 8, 10
Apodized Resolution User selectable: 0.5 cm-1, 1 cm-1, 2 cm-1, 4 cm-1, 8 cm-1, 16 cm-1, 32 cm-1
Scan frequency 6 scans/s @ 32 cm-1
Detector Stirling Cooled MCT (standard)
TE Cooled MCT (application dependent)
Detector temperature 77 K (Stirling cooled MCT)
Source SiC, 1550K
Beamsplitter ZnSe (standard)
Window material ZnSe (standard)
Wavenumber range 600-4200 cm-1 
Temperature stability < 1% per C⁰
Frequency repeatability  < 0.001 cm-1 @ 1918cm-1
Frequency accuracy < 0.06 cm-1 @ 1918cm-1
Short term stability < 0.09%
Maximum signal to noise ratio 50,000: 1 (RMS, 60s, 4 cm-1, at peak response)
Signal sampling 24-bit ADC
Quality Assurance Hardware
Type Internal linear multi-pass cell permanently mounted in beam path. External window removable.
Calibration gas inlet Quick Connect QA Adapter: 1/4″ Swagelok
Calibration gas outlet Screw-in Exhaust Adapter: 3/8″ Swagelok
Path Length 19.2 m
Volume 3.4 L
Maximum sample pressure 1 PSI
Pressure and temperature measurement Integrated pressure and temperature sensor
HMI Touchscreen (standard model)
Digital Interface RJ45 Ethernet LAN Port for local or internet based remote data and access using MODBUS TCP, VNC, and remote desktop.  Spectral data may be stored locally, on a NAS, or disabled. Industrial external wireless option available. Type A USB for data retrieval and peripheral accessories.
Power Connection Environmentally sealed circular Amphenol bayonet connector.
Integrated Computer Embedded industrial PC
Integrated Wind Mapping Three dimesnional ultrasonic anemometer with temperature measurement. Data integrated into CMS data tables and available via MODBUS.
Integrated Data Acqusition External ports with data integration for particulate or ancillary co-located analyzers (TDLAS laser, electrochemical, etc.).
Data Output MODBUS over RS-232, RS-485.  MODBUS over TCP-IP is standard.
Analog Output 8 channel configurable 0-24mA (4-20mA with extended range)

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